When coastal geological expert Brain Atwater began to investigate hints of a major tsunami on the Washington coast that predated the arrival of Lewis and Clark, he turned to Japan to find the most compelling evidence.
Searching through numerous records at the time, Atwater began to uncover details of what likely was a tsunami caused by a Cascadia earthquake originating in the Pacific Northwest in January 1700. Locally, the most notable natural evidence can also be found in the ghost tree forest up the Copalis River, and in similar rivers such as the Johns River to the south. Or it can be traced in salt-marsh evidence along the shore east the Ocean Shores Airport.
“This kind of evidence is really obvious if you know where to look for it and how to make it visible,” said the University of Washington professor and researcher with the U.S. Geological Survey. “It escaped notice for a long, long time in some respects.”
Atwater presented some of his research earlier this month in a lecture at the Ocean Shores Elks Lodge, “Japanese Clues to a Washington Tsunami 100 years before Lewis and Clark.” The lecture was part of the Glimpses series to benefit the Coastal Interpretive Center in Ocean Shores.
Atwater has documented the findings in the 2005 book, “The Orphan Tsunami of 1700,” which estimates a magnitude 9 earthquake in January known as the 1700 Cascadia Earthquake.
Without other documentation, there is scant evidence elsewhere of what might have occurred on the West Coast a century before, according to Atwater. “For an event in 1700, it might as well have been in the time of the dinosaurs,” he said.
Atwater showed slides of other notable tsunamis that struck Japan over time, such as the impact of a tsunami that originated with an earthquake in Chili in 1960. He went through Japanese research of “floods from the sea, not accompanied by shaking from an earthquake in Japan.” Also using Spanish-language records, the Japanese were able to match up tsunami records back to 1586 from the Americas.
Atwater explained how he first began to research the subject while looking at potential earthquake hazards posed by the ill-fated nuclear power plants at Satsop in the 1980s.
“Our history here is so short it doesn’t run the clock long enough for nature to show its hand,” he said. Nature, however, does reveal evidence of the accompanying tsunami: the land drops, tides bring in mud that covers up forest soils, killing trees, and leaving traces of the vegetation that once was there centuries later. The cedar and spruce trees in the Copalis ghost forest were time tested by taking slices of their rings, and Atwater said similar evidence from a 1700 event that can be found in rivers and bays as far south as the Oregon Coast.
Looking at subduction zone earthquakes in general, Atwater explained they don’t happen very often throughout history. “The reason there has been no earthquake since then is that it takes time,” Atwater said. But when it does, it will likely trigger a tsunami that could “come in more like a river or a flood.”
“This sort of detective story then is behind some of the efforts to improve tsunami safety out here,” Atwater concluded.
Read Atwater’s book online: http://ift.tt/wYCiqH
Lecture notes
Because of weather, a planned field trip with Atwater has been rescheduled for 11 a.m. April 25 at Ocean Shores Airport. The lectures resume at 6:30 p.m. March 4 at Ocean Beah Roasters. Matt Longenbaugh speaks on “Where do Tides Come From, and the Ocean in 3-D.”
On April 1, Gene Woodwick, takes up “Logging in Grays Harbor.” Gene is author of a new book, a Daily World columnist, and former director of the Interpretive Center.
Tickets for each lecture are $8. For information, call (360) 289.4617.
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